In the past, the semiconductor industry has utilized silicon carbide to form a variety of transistors including vertical transistors, lateral transistors, metal semiconductor field effect transistors (MESFETs), and metal oxide semiconductor field effect transistors (MOSFETs). One problem with the prior lateral MOSFETs, is the breakdown voltage. Typically, prior lateral MOSFETs have breakdown voltages less than approximately 100 volts. Such low breakdown voltages prevent utilizing the prior lateral MOSFETs in high voltage applications such as power devices for motor controls and power supplies. These type of applications typically require breakdown voltages of at least 150 volts and, preferably as much as 500 volts to 1200 volts. Lateral silicon carbide devices have achieved the 150 volts breakdown voltage and, in addition, silicon carbide devices have about ten times lower on-resistance than comparable silicon devices.
A new and promising technology for very high power is the fabrication of gallium nitride (GaN) devices. However, in spite of unique advantages of GaN based devices, the applicability of GaN vertical devices in power device applications presently seems very difficult to realize. This is due to the lack of GaN substrates that could be used for growing homoepitaxial layers. Further, while GaN appears promising for very high voltage applications no one has been able to fabricate a GaN device with a sufficiently high breakdown voltage.
Accordingly, it would be highly desirable to provide very high voltage GaN devices with a high breakdown voltage and low on-resistance.
It is a purpose of the present invention to provide a new and improved high breakdown voltage heterostructure field effect transistor.
It is another purpose of the present invention to provide a new and improved high breakdown voltage heterostructure field effect transistor with a very low on-resistance.
It is still another purpose of the present invention to provide a new and improved high breakdown voltage heterostructure field effect transistor for use in very high power applications.